Optimization is the action of making the best or most effective use of a situation or resource. Designing chilled water systems Typically used for cooling and dehumidifying a building’s air, chilled water (CHW) systems circulate it throughout a building or campus complex. The chiller is the section of the system where an exchange of heat occurred between the water that goes to the building and the evaporator. Courtesy: SmithGroup. The most common types of chiller plant pumping arrangements are constant flow, primary-secondary variable flow and variable primary flow systems. The chilled water produced reduces the load on the central chillers. Space heating systems are normally designed at 140°F supply water temperature. Learn about the impact of pumping schemes and plant optimization of chilled water systems. Chilled Water Distribution*. Campus Chilled Water System:UNK, UNL and UNO campuses are served by central utility plants operated by the Utility and Energy Management (UEM) department. Figure 2: In this waterside economizer system diagram, when the economizers are optimized alongside each of these influencing systems, then the potential benefits of waterside economizing increase. Adding ceiling fans into the space, which with modest air-speeds support thermal comfort even up to 78°F room setpoints may increase that load shifting flexibility even more, potentially allowing 100% of cooling hours to be met with full waterside economizer. Demand Flow is an HVAC optimization solution that reduces energy costs and ensures ongoing operational efficiency, with healthy financial returns and long-term value. Courtesy: SmithGroup. Search Products And Discover New Innovations In Your Industry!! Search Products And Discover New Innovations In Your Industry, Scott Battles, Jonathan Hulke and Stet Sanborn. 1. During winter operation, the heat recovery chiller can operate to meet the process cooling loads of the hospital while also providing hot water to reduce the demand on the boiler plant. The waste heat that is normally rejected to the outdoors can be recovered and used in applications where heat is required, such as heating domestic water or terminal reheat. This is typically limited to inputting project specific equipment performance data into the control software, which will, in turn, sequence a specified number of chillers, cooling towers and pumps based on operational “sweet spots” to meet building load. Scenarios like this can be difficult for operators to accept after operating in a more traditional way for many years. Heat recovery chillers can be very effective in health care facilities. There are several factors to consider including: Existing or proposed design delta T, or lower water return temperatures. These can be in many forms when they are connected to a chilled water distribution system. A more complex chilled water cooling system configuration can consist of multiple chillers, multiple pumps, cooling towers, heat exchangers, and all sorts of valves to redirect flow according to the heat load inside of the building. Figure 3: In Oakland, Calif., a 100% waterside economizer system can produce 55°F chilled water without the chiller operating. The components of closed and open hydronic systems. The real beauty of waterside economizers is on display when they are paired with mild temperature chilled water systems. This allows the software to sequence the equipment so it can operate most efficiently for longer periods of time throughout the year, thus providing a greater overall percent reduction in energy usage. Essentially, the building owner gets heat energy at virtually no cost because it is a byproduct of the cooling process. The waste heat that is removed from the chilled water loop is captured in a hot water loop that is used for heating. Heat recovery chillers can provide energy savings in facilities where there is a need for simultaneous heating and cooling, such as hospitality and health care facilities. Chilled-water pump; 17 Distribution piping; 18 Pumping arrangements; 19 Condenser-Water System ~ Cooling tower ~ 20 Condenser-water pumping arrangements; 21 Unit-Level Controls; 24 Application Considerations. 3300 0 obj <>stream The water leaves the chilled water evaporator at 45°F or 7°C. Increasing the temperature difference between the chilled water supply and return takes full advantage of the total capacity of the chillers; variable primary flow systems typically have a lower first cost than primary-secondary variable flow systems. To truly understand the benefits of chiller plant optimization, it is recommended to complete a baseline analysis of the existing system or new installation to help validate the benefits to system performance. Figure 1: At the Ford Field chiller plant in Detroit, evaluating the existing chilled water coils at varying chilled water supply temperatures is required. The benefits of waterside economizers increase with warmer chilled water supply temperatures, so they pair especially well with hydronic systems such as radiant cooling, chilled beams and dedicated outdoor air system fan coil boxes, where air-side economizers are either not applicable or not feasible. Understand how and when to consider a waterside economizer. A traditional chilled water design approach in a building with high internal loads, such as an office building results in a low percentage of operating hours that can be used for 100% economizer mode. Select condenser water distribution . The distribution system can pump up to 100,000 gallons of chilled water per minute through more than 22 miles of underground piping and 150 individual building bridge systems. The first strategy is a chilled water supply temperature reset control sequence (ASHRAE 90.1-2019 Part 6.5.4.4), which should be deployed on all waterside economizer systems. Minimum flow rates are important to maintain in the cooling towers to ensure that the cooling tower fill remains fully wetted. An important aspect to note is owner and plant operator buy-in to the software to allow it to operate as intended. Chillers and constant flow primary pumps are enabled in pairs, making the primary flow rate a step function. system; 4. Evaluating the existing chilled water coils at varying chilled water supply temperatures is required to determine if the coils must be replaced or what temperature differences can be achieved with the existing coils (see Figure 1). Typically, these systems are working in parallel with a DOAS system, which is handling dehumidification with a direct expansion system or standalone low-temperature chilled water coil supplied by a separate system. Thermal energy storage systems maximize the use of nighttime charging of the storage tanks when outside wetbulb temperatures are at their lowest, allowing for low cost chilled water production using nighttime off-peak power rates. There are different levels of optimization currently being applied in the industry ranging from simple sequencing of the equipment to the installation of electrical usage metering to enable system adjustments in real time through software. Minimum flow rates must also be maintained within the condenser section of the chiller. Typically, heat recovery chillers are designed to provide hot water for space heating at 105°F to 110°F. How Chilled Water Air Conditioning Works. Figure 4: In this example, 80% of annual hours can have the cooling load met with waterside economizer when combined with close approach cooling towers. Traditional chilled water systems producing 42°F to 44°F chilled water will be limited in how many hours they can take advantage of 100% waterside economizer, especially when the engineer has specified a traditional cooling tower approach of 6°F to 7°F and required a plate and frame heat exchanger with its 1°F to 2°F approach. After completing the course, you should know: 1. When the water has been used and has warmed, it is returned to a chiller plant to be chilled again. Although the typical thermal storage medium is water (or ice for low-temperature chilled water systems), recent research from the University of California, Berkeley’s Center for the Built Environment has shown significant flexibility in mass-radiant cooling systems to support load shifting through controls manipulation alone and the inherent thermal mass of the slab. A holistic approach to optimizing chilled water and air distribution systems. To counter this overcooling, terminal reheat is required. One system is always distributing chilled water to the units and returning it to the chiller. Chilled Water Distribution System. When the pumping capacity matches the thermal load, it increases the temperature difference between the chilled water supply temperature and chilled water return temperature. At each building the chill… † Meet its needed evaporator flow requirements independent of other chiller operation. Total chilled water distribution system volume is 1.5 million gallons +. Bypass line … From an owner’s perspective, implementing some form of chilled water plant optimization can be appealing for a couple different reasons. Chilled water is centrally produced and distributed throughout the campus, and this district cooling system shall be utilized wherever possible. Besides selecting close approach towers, there are several other strategies that can be deployed to increase waterside economizer hours, reduce chiller hours and possibly eliminate the need for compressor cooling all together. HRCs can be used to meet or supplement the local building heating requirements while utilizing the benefit of the simultaneous cooling to cool the building or export this by-product to the campus chilled water distribution loop. The heat is then rejected from the condenser water loop to the outdoors by a cooling tower. Table 6-1 Chilled Water Distribution System ..... 6-3 Table 6-2 Advantages and Disadvantages of Primary-only vs. Primary-secondary ..... 6-5 Table 6-3 Impact on First Costs and Energy Costs of Chilled Water Campus-Wide System:A campus-wide central chilled water system has been developed in recent years and is being expanded to serve additional cooling loads as need arises and opportunity affords. Here, a set of constant speed pumps distributes fixed quantity of water at all times and the temperature varies to meet the load. h�b```��,�R� cb�FdQ&!EAEQ6�����m�uhp0�������I3�!��s�O��(i����^`����e|%��Y����/dM0��fg|}�g�ʄٳ�3%J}�u�sa���+����F��G�����.��V�d�j r��F��o\SW=U�(�����cG!��H;G�s���!%�Ӈ�.t�(pqzx$���c�P��]FIMFP`G鴲��@m3 Review how and when to deploy a heat recovery chiller. Select cooling tower type, speed control option, efficiency, approach . Select chilled water temperatures, flow rate, and primary pipe sizes; 3. Courtesy: SmithGroup. The district cooling system is comprised of four major subsystems; the production system, the distribution system, the building bridge system, and the building cooling system. Another application such as service water preheating normally uses heat recovery water temperatures of 85°F to 95°F. Currently, some controls manufacturers integrate plant optimization into their standard control package. endstream endobj startxref A standard water-cooled chiller operates to remove heat from a chilled water loop and transfers that heat into a condenser water loop. Case 3: Conversion of a Parallel-piped System to Series, and from “Conventional” to Increased ΔT. How to match pumps to systems. The type of building, climate and load profile are contributing factors into whether one or all of those strategies should be considered. 0 There are several factors to consider including: The impact of these criteria will guide the chilled water plant production decisions and the most efficient pumping arrangement. As radiant systems, chilled beams and DOAS fan coil boxes are designed for sensible cooling only, they do not require low-temperature chilled water and in fact don’t want chilled supply water temperatures which could result in condensation. Selecting the lowest practical heating temperature reduces the chiller lift and results in the chiller operating more efficiently. Like all heating, ventilation and air conditioning system selections, it is important to understand the impact on all systems together, including building enclosure, building massing, load profile and occupant comfort expectations. Additionally, waterside economizer systems pair well with thermal energy storage systems, especially mild temperature systems serving sensible only cooling systems. Chilled-water distribution system Chilled water is circulated through fixed piping —most commonly steel, copper, or plastic —that connects the chiller with various load terminals. Chiller. The other is distributing hot water to the units and return- ing the water to the boiler. Existing or proposed design delta T, or lower water return temperatures. Type of chilled water system control valves, installed or proposed (three-way or two-way valves). For many buildings, the chilled water system provides tremendous potential for creating energy savings. What this means for a chilled water plant, as dictated by ASHRAE Standard 90.1 and the International Energy Conservation Code, is controlling the associated equipment, whether new or existing, to operate as efficiently as possible and ultimately consume the least amount of energy, while meeting the building needs. The existing chilled water coils were likely not selected to perform with the 2019 edition of ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings required 15°F temperature difference between entering and leaving water temperature. Select chilled water distribution . So, the elevated chilled water temperatures are ideal. temperature, and make cooling tower The expense to maintain the BTU’s, or to chill the return lines are far higher than the cost to reheat return lines on a heated system. Operating the variable primary pumps in parallel to match the optimum efficiency point on the chilled water distribution system curve is an effective way to minimize the system pumping energy. Maximum and minimum chilled water supply temperatures. Even with the potential concerns, variable flow in the condenser water system is still a viable option and can further reduce the overall kilowatt per ton of chiller water produced throughout the entire range of plant operation. Chilled water distribution. The chilled water distribution system includes more than 6 miles of are direct-buried, ductile iron pipes up to 30 inches in diameter. How centrifugal pumps operate. If the flow rate In the secondary side is low then some chilled water will flow into the secondary and some will recirculate back to the chillers. This chilled-water is then circulated through the entire building by the use of a pump. The 4-pipe water distribution system is actually two, 2-pipe systems in parallel; each system consisting of its own supply and return main. There is the obvious reduction in energy usage, which directly translates to dollars saved with the utility company. You will develop an understanding of the basic concepts of hydronic system operation and design including piping systems, pipe materials and fittings, centrifugal pumps, terminal units, expansion tanks and water chillers. facilities have plants that make chilled water and distribute it to air-handling units (AHUs) and other cooling equipment For example, referencing strategies in ASHRAE 90.1, this could mean using pumps with integral VFDs for a variable flow system or using chilled water reset in a system with integrated waterside economizer as described in the section below. The district cooling system is comprised of four major subsystems; the production system, the distribution system, the building bridge system, and the building cooling system. The header supplies four pipelines that go down the mine with draw-off points at depths of 1000 m and 2000 m. %PDF-1.6 %���� Establishing a baseline is an important aspect of this process especially as it relates to return on investment as there is a premium associated with chilled water plant optimization. endstream endobj 3278 0 obj <. Pressure drop is overcome by the use of a chilled-water pump. Two-pipe HVAC chilled water systemsare reasonably energy efficient. For the vast majority of chilled water plants, the energy efficiency of the plant can be maximized by varying the pumping capacity to match the required thermal load. Instead of operating in the 42°F to 44°F range, these systems tend to operate around 54°F to 58°F and supply radiant cooling systems, chilled beams or sensible only DOAS fan coil boxes. The different types of pipe used in hydronic systems. Understanding the actual building load so that equipment can be right-sized is critical. Terminal equipment, proposed or installed. As soon as all chilled water valves are less than 100% open, the BMS will linearly reset the chilled water supply temperature upward until the first valve must open 100% to satisfy the local load. These pumps are a very cost-effective way to limit the number of field mounted sensors and controls while minimizing pump energy usage. As a result of minimum air change rates, rooms are often provided with more air than is needed for cooling the space. The distribution pumps (primary pumps for the p-only system and secondary pumps for the p-s system) are fitted with variable speed drives (VSDs). The load study for a new building is easier to achieve. Strategies such as chiller plant optimization, water side economizer and heat recovery chillers can create positive results by improving overall plant efficiency and reducing energy costs. To help with infection control, clinical spaces within health care facilities are required to have minimum air change rates. Changing the three-way control valves to two-way control valves and evaluating the use of two-way pressure independent control valves will solve many of these distribution issues. The greatest impact on the cost of a large central chilled water system is provided by the temperature spread between the supply and return, usually termed the Delta T The central system designer seeks to achieve a large Delta T 14 [degrees]F or 16 [degrees]F are common. These increased supply water temperatures greatly increase the available hours for 100% waterside economizer, showing economizer hours with a traditional approach cooling tower (see Figure 3). 16 Chilled-Water Distribution System. It is common that equipment in older chilled water plants were selected based on the peak load and not the total operating range of the plant. The system uses 3-way control valves at air handler coils that allow some water to bypass the cooling coil during part load conditions. The chilled water distribution system must be evaluated before a new chiller plant design or existing chiller plant upgrade can be finalized. Upgrading an existing constant flow or primary-secondary flow chilled water plant to a variable primary flow chilled water plant that is connected to a distribution system with three-way valves would result in a constant flow system with a low delta T, for a large range of the chilled water plant’s operation. What varia… Underground chilled water piping systems are typically used to cool buildings. As a result, reheat energy has historically been one of the largest end uses of energy in a hospital, representing 25% to 30% of the total annual energy usage depending on the climate zone. That flexibility has shown that in some instances, active cooling into the slab may shift upward of 12 hours separation from the time of peak load in the space, while still keeping the space operative temperature with the comfort range expected by ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy. When waterside economizers are optimized alongside each of these influencing systems, then the potential benefits of waterside economizing only increase (see Figure 2). Waterside economizer uses the evaporative cooling capacity of the cooling tower to produce cold water that is exchanged through a heat exchanger to provide chilled water that offsets the need for mechanical cooling. Maximum and minimum chilled water supply temperatures. Select condenser water tempera-tures, flow rate, and primary pipe sizes; 5. Chilled water is distributed at 42 degrees F to more than 80 buildings from the Power Plant and the North Chiller Water Plant to provide the cooling for campus. It is possible to design chilled water systems that meet the thermal comfort demands of the building and achieve operational and energy efficiencies that can significantly decrease ongoing operational costs. The best results from optimization are achieved when all of the system equipment is sized appropriately to meet the actual chilled water demand and not over or undersized. By Scott Battles, Jonathan Hulke and Stet Sanborn, ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings, University of California, Berkeley’s Center for the Built Environment, ASHRAE Standard 55: Thermal Environmental Conditions for Human Occupancy, Weekly merger and acquisition update: January 15, 2021, Top 5 Consulting-Specifying Engineer articles: January 8-14, 2021, Understanding changing data center metrics, Ultra-low temperature storage considerations for COVID-19 vaccines, Case study: University science building control systems, Neurologic institute building trying to redefine patient care. Centrally produced and distributed throughout the campus, and this district cooling system shall be wherever... Rejected from the condenser water tempera-tures, flow rate ( from supply to return in. Fill remains fully wetted 55°F chilled water produced reduces the chiller lift and in. 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